1. Technical Field of the Invention
This invention relates to a process for the manufacture and purification of methyl tertiary butyl ether. More particularly, this invention relates to a process for reducing the formation of tertiary butyl alcohol in a finishing reactor in a process for the manufacture of methyl tertiary butyl ether (MTBE) from tertiary butyl alcohol (TBA) and methanol (MeOH). Still more particularly, this invention relates to a process for the manufacture of MTBE from TBA and MeOH wherein by-product isobutylene formed by the reaction of TBA with MeOH is reacted with methanol in a finishing reactor under substantially anhydrous conditions to selectively provide additional methyl tertiary butyl ether with the reduced formation of tertiary butyl alcohol.
2. Prior Art
In U.S. Pat. No. 4,144,138 (1979) to Rao et al., there is disclosed a method for recovering methyl tertiary butyl ether from etherification reaction effluent by azeotropic distillation to recover methanol-ether azeotrope overhead which is water-washed to give pure ether extract, the latter being azeotropically distilled to yield ether-methanol overhead which is recycled to water washing.
The preparation of methyl tert-butyl ether from methyl and tert-butyl alcohols is discussed in S. V. Rozhkov et al., Prevrashch Uglevodorodov, Kislotno-Osnovn. Geterogennykh Katal. Tezisy Dokl., Vses. Konf., 1977, 150 (C. A. 92:58165y). Here the TBA and methanol undergo etherification over KU-2 strongly acidic sulfopolystyrene cation-exchangers under mild conditions. This reference contains data on basic parameters of such a process.
Kruse et al. U.S. Pat. No. 5,243,091 discloses a method for the preparation of methyl tertiary butyl alcohol wherein a mixture of methanol and tertiary butyl alcohol are catalytically reacted to form a reaction product that is separated into a first lighter distillation fraction comprising isobutylene, methanol and methyl tertiary butyl ether and a second heavier distillation fraction comprising methanol, tertiary butyl alcohol and water, wherein the first distillation fraction and a first recycle isobutylene fraction are reacted to form an isobutylene conversion product that is charged, together with recycle isobutylene to a methanol extraction zone and countercurrently contacted with water to provide an overhead raffinate comprising aqueous isobutylene, and wherein the isobutylene is recovered and recycled.
Gupta U.S. Pat. No. 5,292,964 discloses a method for the preparation of methyl tertiary butyl ether wherein a mixture of methanol and tertiary butyl alcohol are catalytically reacted to form a reaction product containing the water of etherification and at least one mol of methanol per two moles of methyl tertiary butyl ether, wherein the reaction product is fractionated to separate a lighter methanol and methyl tertiary butyl ether fraction from the water and tertiary butyl alcohol and wherein the methanol in the lighter distillation fraction is reacted with isobutylene to form additional methyl tertiary butyl ether.
Gupta states that it is essential to provide a reaction product containing at least one mol of methanol per two moles of methyl tertiary butyl ether, so that water is separable from the methyl tertiary butyl ether in the fractionating column to provide a lighter distillation fraction substantially free from water.